The problem of discriminating and counting the number of objects randomly distributed in a visual field is encountered in many technologies. The determination of: size distribution in powders, particulate matter in gasses, events represented by grains in nuclear emulsions, cloud cover in satellite photographs, and bacterial colonies in culture are some examples which are approached by visual counting. A whole class of instruments for systematizing, automating, and reducing the errors of manual counting are commercially available for many applications.
In those situations where object discrimination is simply based on contrast and size, the number of objects in a size range may be simply related to the spatial frequency content of the visual field containing the objects. A discrimination technique based on far-field diffraction pattern analysis, requiring detailed knowledge of the scattering function, is described by W. L. Anderson and R. E. Beissner in "Applied Optics," 10, 1503 (1971), and J. P. Meric, et. al., in "Optical Communication," 10, 266 (1974). Some pattern recognition techniques, using digital image processing, depend upon the spatial frequency signatures of the objects that are to be counted, as discussed by B. C. Partridge, Proc. 16th Annual Technical Meeting of the Society of Photo-Optical Instrumentation Engineers, 4, 207 (1973). A simple method, long used in missle guidance, for measuring image spatial frequencies by means of rotating reticles has been described by G. F. Aroyan in "Proceedings of the IRE," , 47, 1561 (1959).
The present disclosure provides an analysis of rotating reticle spatial frequency selection as it is applied to counting automation. An example of the utility of this technique applied to the difficult problem of monitoring the growth of irregularly shaped granulocyte precursor cell colonies distributed in a turbid semi-solid medium is disclosed.